1. Field of the Invention
The present invention relates to a propeller pitch-change mechanism for a vehicle, such as aircraft, and more particularly to such a mechanism for automatically changing the pitch of propeller blades without the necessity of external power and which does not require operator or pilot adjustment.
2. Brief Description of the Prior Art
In the general field of propeller blade pitch control for vehicles, such as aircraft and boats, efficient operation of the vehicle requires that the propeller pitch be adjusted for an optimum angle of attack for each vehicle velocity so that the blades absorb the maximum power at a given air speed or boat speed. With respect to aircraft, this consideration provides low blade angles (low pitch) at low aircraft air speeds such as at aircraft takeoff, and at high pitch for aircraft cruising speeds.
In order to provide proper blade angle, current propeller designs of infinitely adjustable pitch mechanisms are activated by external power sources, such as hydraulic pressure or by electric motor. The external power sources may be assisted by centrifugal counterweights or the like. Constant speed propellers change their pitch angle to match air speeds at a constant engine RPM selected by the pilot. Other propellers have two pitch angles, one for climb and one for cruise, which are selected by the pilot during flight, while others have to be manually set on the ground. Non-automatic pitch change mechanism usually employs heavy motors and hydraulic systems that require special circuits, pressure lines or other added parts, all of which are weighty components and increase the overall weight and complexity of the mechanism. Particularly in aircraft installations, it is most important to keep weight and complexity as low as possible.
Some attempts have been made to provide proper adjustable pitch control which are disclosed in U.S. Pat. Nos. 3,635,583; 3,560,110; 2,396,630; 1,982,283 and 4,304,524. Although such mechanisms and adjustment means may adjustably control the pitch of propeller blades, such means are not automatic and still encompass problems noted above. In some instances, torsion springs are employed but such engine torque pitch control adjustment is relatively insensitive to automatic adjustment and is subject to material fatigue.
Therefore, a long-standing need has existed to provide a propeller pitch-change mechanism for vehicles such that the operation of the mechanism is completely automatic and does not require external power nor intervention by the pilot.